Parental Care and Investment

Abstract

Parental care is common throughout the animal kingdom, and much variation exists among species in how, and how much, parents
care for their offspring. In most species, females care more; in others, males care more and in some, caring is more or less
equally shared between the sexes. Several hypotheses have been proposed to explain patterns of parental care within and among
species. These hypotheses invoke factors such as the relatedness (parentage certainty) of each parent to the brood; the sex
ratio at maturation; the strength of sexual selection faced by each sex and the exact nature of any trade‐offs between caring
and other activities. Work is still ongoing to develop an overarching hypothesis to explain the various patterns observed.

Key Concepts

Among species there is much variation in how, and how much, parents care for their offspring.

Differences between the sexes in parental care can evolve if one sex has more to gain and/or less to lose by providing care.

Coevolution between parental care and sexually selected traits may amplify small initial sex differences in caring over time.

Individual decisions on the optimal parental investment can lead to conflict between parents, as well as between parents and
offspring.

In some species, care of the offspring is not the exclusive responsibility of the parents but is shared among members of a
group, termed cooperative breeding. In other species, adults sometimes take care of unrelated offspring, either willingly
(as in adoptions) or unwillingly (as in brood parasitism).

Within species, parents sometimes adjust the amount of investment in offspring based on cues from their partner or from the
offspring themselves.

Figure 1. Factors affecting the benefit and cost of care for a parent. A mutant parent providing more than the usual amount of care
to a given brood is favoured by selection if the associated fitness benefit is greater than the cost. Black arrows indicate
causal effects of the focal parent's behavioural change and are marked at their base by ‘+′ (or ‘−′) if the behavioural change
increases (decreases) the quantity to which they point. Blue arrows show how other factors modify these causal effects: when
fusing with black arrows, they indicate that the quantity represented by the blue arrow strengthens the causal effect represented
by the black arrow. Blue arrows marked at their base by ‘+′ (or ‘−′) indicate that the quantity from which they start increases
(decreases) the quantity to which they point. Sex differences in the benefit of care may arise because of parentage certainty
or care ability. Sex differences in the cost of care may arise because sexually selected traits put one sex at greater risk
to die when caring; or because parents of one sex have higher future fitness expectations (hence having ‘more to lose’ in
the event of their death) or because caring affects mating success or body condition in ways that have different fitness consequences
for each sex.

McNamara J and Wolf M (2015) Sexual conflict over parental care promotes the evolution of sex differences in care and the ability to care. Proceedings of the Royal Society B: Biological Sciences 282: 20142752.